Nonlinear flight control design using sliding mode disturbance observer-based constraint backstepping

This paper presents a sliding mode disturbance observer-based constraint backstepping control approach (CBS/SMDO) to control a cargo aircraft during heavy cargo airdrop operation. The CBS/SMDO controller is capable of dealing with parametric uncertainties, external disturbances, and unmodeled dynamics in the presence of state/control constraints. The super-twisting second order sliding mode disturbance observer (SOSMDO) is utilized to compensate for the overall uncertainties, avoiding high control gains. The SOSMDO is much simpler than the neural networks-based estimator and could provide asymptotic convergence of the estimation error to zero in finite time. The closed-loop stability is guaranteed in the sense of Lyapunov. The proposed CBS/SMDO controller is applied to the airdrop flight control design on a nonlinear six-degrees-of-freedom transport aircraft model in a low attitude tandem extraction airdrop scenario. Simulation results demonstrate the feasibility of the CBS/SMDO method.